The invention relates to a clamping tool for clamping a workpiece to a support by means of a bar system constructed of a number of mutually pivotal bars and comprising an activation bar for at operation making the bars pivot mutually between an initial position and a locking position, a clamping bar having at least one thrust shoe for pressing against the workpiece in the locking position of the bar system, and a base for mounting the bar system on the support.
Several different designs for such clamping tools are known that however have that in common that they are only able to exert pressure to a workpiece in one specific direction. Such a design is e.g. known from FR 260 1609. This invention relates to a system for immobilising a component located on the work table of machine tools.
In many cases, it is however necessary to clamp the workpiece in two directions, e.g. both a vertical and a horizontal. This is e.g. the case when a number of workpieces are to be welded together to a whole in a welding fixture, and each workpiece for this purpose must be positioned in two direction in order to obtain the accuracy that normally is required of such welded objects. Instead of one set of clamping tools, two sets have to be used, namely one set for clamping the workpieces in one direction and a second set for clamping the workpieces in a second direction.
The operation of the many clamping tools is labour-consuming and increases thereby the production costs. The doubling of the number of clamping tools furthermore means that the welding fixtures are expensive to produce.
The object of the invention is to eliminate the above disadvantages of the known clamping tools by providing a clamping tool of the kind mentioned in the opening paragraph that is arranged in such a way that it is able to simultaneously act on a workpiece which is to be clamped to a support with compressive forces in at least two directions.
The novel and unique features according to the invention, whereby this is achieved, is the fact that the bar system comprises at least two toggle joints, that at lest two of these toggle joints are arranged to simultaneously or almost simultaneously assume their dead point positions when the bar system at activation is taken from the initial position to the locking position, and that said two toggle joints form an angle with each other in the dead point position.
By means of this arrangement of the clamping tool, a thrust shoe on the clamping bar can be made to act on a workpiece with a pressure in one direction while a second thrust shoe on the clamping bar simultaneously can act on the same workpiece with a pressure in a second direction.
A number of workpieces, which e.g. are to be welded together to form a whole in a welding fixture, can now be clamped securely and precisely in the fixture by means of normally half as many clamping tools as is required when conventional clamping tools are used. Thereby the task of clamping the workpieces and subsequently removing the finished, welded object from the fixture is facilitated and made less expensive, just as the costs for producing the fixture are reduced considerably.
The two joints of each toggle joint can according to the invention together form an angle which in the initial position of the bar system is pointing the point in the opposite direction of the thrust shoe, and the bar system can furthermore be arranged in such a way that its two toggle joints are put into their dead point positions by taking the bar system from the initial position towards the locking position. When the toggle joints during this approach the dead point positions, it will using a moderate manual force application on the handle of the bar system be possible to act on the workpiece that is to be clamped with considerable compressive forces in two direction at the same time. The maximum effect on the workpiece is obtained in the dead point positions in which the position of the whole bar system however is labile.
In the locking position of the bar system, each toggle joint is therefore taken beyond the dead point to a position in which its two joints together form an angle the point of which is pointing towards the thrust shoe. To maintain the great force application on the workpiece that is to be clamped, said angle is only a little smaller than 180xc2x0, e.g. 1xc2x0-2xc2x0 smaller.
In an especially expedient and effective embodiment, the bar system according to the invention can comprise a first swivel connection for pivotally journaling one end of the activation bar in the base while the other end of the activation bar is free and serves as handle of the clamping tool; a rocking bar which at one end is pivotally journaled in the base via a second swivel connection which is nearer the at least one thrust shoe than the first swivel connection, and at the other end is pivotally journaled in the clamping bar via a third swivel connection; a first toggle joint having a first joint which at one end is pivotally journaled in the clamping bar via a fourth swivel connection which is farther from the at least one thrust shoe than the third swivel connection, and at the other end is pivotally journaled in the activation bar via a fifth swivel connection, and a second joint consisting of the part of the activation bar that is extending from the fifth to the first swivel connection; and a second toggle joint having a first joint which at one end is pivotally journaled in the rocking bar and/or clamping bar via a sixth swivel connection and at the other end is pivotally journaled in the activation bar via a seventh swivel connection which in the locking position of the clamping tool is nearer the at least one thrust shoe than the first and fifth swivel connection, and a second joint consisting of the part of the activation bar that is extending between the seventh and first swivel connection.
In one embodiment, the first joint of the second toggle joint can be pivotally connected to the clamping bar with the same swivel connection as the rocking bar while the first joint of the second toggle joint in a second embodiment can be pivotally connected to the rocking bar via a swivel connection another place on the bar. The first and second toggle joint can pass the dead point positions simultaneously when the bar system is taken from its initial position to its locking position. Thereby, the workpiece to be clamped is affected simultaneously in the two different pressure directions of the clamping tool. If the two toggle joints do not get to pass the dead points simultaneously, the workpiece can be clamped in one direction before it is finally clamped in a second direction. One of or each of the first joints of the two toggle joints can be shaped as a U with a bottom and two sides so that the bar system can be constructed compactly together.